In previous studies, we characterized the actions of arachidonate 5-, and 15- lipoxygenase (LO) products {leukotrienes (LTs and lipoxins (LXs)] in the rat nephron. Subsequently, we and others provided evidence supporting a role for LTs in promoting leukocyte infiltration/activation, proteinuria, mesangial proliferation and functional deterioration during experimental glomerulonephritis in the rat. Formation of LTs and LXx in glomerular inflammation arises from total synthesis within neutrophils/macrophages, or through transcellular metabolism of the leukocyte-generated intermediate, LTA4, by endothelial and mesangial cells and infiltrating platelets, to yield LTs C4, D4, B4, and lXA4.LT biosynthesis is regulated tightly; a major increase occuring in the first 48 hrs of injury, followed by suppression to pre-injury levels, suggesting the activation of endogenous counter-inflammatory pathways. We have discovered evidence that the 15-LO products, LXA4 and 15-(S)-hydroxyeicosatetraenoic acid [15-(S)-HETE}, exert potent anti-inflammatory actions during the neutrophil and macrophage- mediated phases of glomerular immune injury. These include direct inhibition of LT synthesis and actions. Significantly, the activities of 15-LO products extend beyond LT antagonism to a generalized down-regulation of neutrophil chemotaxis, adhesion, and activation, as well as marked suppression of macrophage activation. Here, we propose to examine the mechanisms underlying the regulation of biosynthesis and pathophysiologic significance of these endogenous pathways of leukocyte activation and inactivation during glomerular inflammation. Specifically, we will use human blood monocytes (PEM) and mesangial cells (MC) to test the hypothesis that specific cytokines released from macrophages and lymphocytes play a crucial role in effecting the switch in the net balance from pro- to anti- inflammatory lipid mediator release, as glomerular inflammation progress from acute to subacute phases. Our findings demonstrate direct regulation of the levels of mRNA encoding for 5-LO, 15-LO, LTA4-hydrolase and five- lipoxygenase activating protein (FLAP), by interleukin 1b(IL-1b), IL-4, IL- 13, and g-interferon in PBM and MC, thereby providing a mechanism for the regulation of eicosanoid synthesis in leukocytes, as well as via transcellular routes. We will couple these studies with in vivo models of glomerulonephritis in rats and mice in which the pathophysiologic relevance of these interactions is tested. We will assess glomerular functions and histologic changes during glomerular injury in 5- and 15-LO gene-deleted mice, and in glomerulonephritis rats in which renal eicosanoid enzyme or cytokine gene expression are manipulated by in vivo transfection techniques. Insight into the regulation of the endogenous balance of pro- and inflammatory influences during glomerulonephritis may provide an opportunity for the design of interventional strategies aimed at arresting immune complex-initiated diseases through preferential expression of anti- inflammatory mediators.